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Lecture Leonas Valkunas


25 november 2008 FWN-Building 5113.0202, Nijenborgh 4, 9747 AG, Groningen
Speaker: Prof. Leonas Valkunas
Affiliation: Institute of Physics, Vilnius, Lithuania
Title: Exicton dynamics in seminconducting single-walled carbon nanotubes
Date: Tue Nov 25, 2008
Start: 10.00
Location: FWN-Building 5113.0202
Host: Paul van Loosdrecht
Telephone: +31 50 363 8149


To define the origin of the electronic excited states of single-walled carbon nanotubes, femtosecond fluorescence up-conversion and frequency-resolved transient absorption measurements were used for selective excitation/probing of particular nanotubes in a micelle-dispersed preparation enriched with individual nanotubes. Analysis of the temporal and intensity profiles of the transient signals enable us to unambiguously identify the excitonic nature of elementary excitations in semiconducting nanotubes, and the predominant dynamical process as a remarkable manifestation of exciton-exciton annihilation [1]. Our studies convincingly support the conclusion that the longest wavelength electronic excitations are of excitonic origin. A satisfactory description of the decays obtained at various excitation intensities, however, requires a time-independent annihilation rate that is valid only for extended systems with dimensionality greater than 2 in conjunction with diffusive migration of excitons. We resolved this apparent contradiction by developing a new stochastic model, in which we assumed that the exciton states in semiconducting nanotubes are coherent, and the multiexciton manifolds are resonantly coupled with other excited states, which decay by subsequent linear relaxation due to electron-phonon coupling [2]. The formalism derived from this model enables a qualitative description of the experimental results for different single-walled carbon nanotubes. Photon-echo experiments were also obtained and the relevant theoretical model explaining the observations is developed. 



1.      Y.-Z. Ma, L. Valkunas, S. L. Dexheimer, S. M. Bachilo, G. R. Fleming, PRL 94, 157402 (2005).

L. Valkunas, Y.-Z. Ma, G. R. Fleming, Phys. Rev. B. 73, 115432 (2006).

Laatst gewijzigd:22 oktober 2012 14:30